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BIOS and UEFI
What is BIOS? BIOS stands for Basic Input Output System It is "a set of computer instructions in firmware which control input and output operations." It performs hardware initialization and runtime services for OSs and programshttps://en.wikipedia.org/wiki/BIOS Location It comes preinstalled on a BIOS chip on a computer's board Modifying the Settings f you change your BIOS settings, the changes will be recorded on the CMOS chip. The CMOS is non-volatile, meaning it is saved regardless of whether the computer is on or not. In fact, it has its own power source. Removing the CMOS battery will cause the BIOS to be reset. File The file menu allows you to * Review system information * Set the date and time * Save or discard changes to the setup program Storage The storage menu allows you to * Get storage device information * Configure and test storage devices * Select boot options Security The security menu allows you to * Set passwords * Set security settings for system devices * View the System IDs for the computer Power The power menu allows you to configure power management features Advanced The advanced menu allows you to * Select power-on options * Select bus options * Select device options https://support.hp.com/us-en/document/bph07110 System POST POST stands for Power On Self Test. It checks for hardware failures.https://computer.howstuffworks.com/pc3.htm # Power is turned on # The chipset waits for a Good Power Signal ## A chipset controls the communication between parts of the motherboard # BIOS stored in ROM chip runs # Hardware is identified and each device is initialized ## If devices are missing or not working, computer may beep or display an error message. ### A list of POST beep codes can be found herehttps://whatis.techtarget.com/definition/POST-Power-On-Self-Test ## Video is initialized ## Other hardware is initialized ### Each device may have its own BIOS # Amount and type of system memory identified ## SSD ## HDD ## HHDhttps://www.minitool.com/lib/hard-disk-1.html # Memory and drive parameters are set # Plug and Play devices are configured ## The memory requirements are determined for each # BIOS assigns resources to DMA channels and IRQs.https://www.youtube.com/watch?v=ZplB2v2eMas https://www.cs.rutgers.edu/~pxk/416/notes/02-boot.html Boot Sequence Once the POST is completed, the BIOS will begin checking hardware for boot programs. The BIOS loads the boot sector of the hard disk. This is called the Master Boot Record.http://www.linux-magazine.com/Online/Features/Coping-with-the-UEFI-Boot-Process A bootloader is a small program that will start a larger program, the operating system https://www.cs.rutgers.edu/~pxk/416/notes/02-boot.html A sector is the smallest amount of data that is stored. A boot sector contains machine code that is loaded into RAM.https://en.wikipedia.org/wiki/Boot_sector Once it finds the boot loader, BIOS hands over control to the boot loader and the boot loader loads the OS into RAM memory. Loading the OS The boot record loads the initial system file into RAM. The initial system file will continue loading the OS. A system configuration file will now be loaded. The system configuration file will load specific operating files such as drivers. Another important file is win.ini or autoexec.bat which tells the OS which applications or programs to load. The OS loads and waits for the user inputhttps://searchwindowsserver.techtarget.com/definition/boot. BIOS Simulation https://download.lenovo.com/bsco/index.html UEFI UEFI began replacing BIOS in 1998. UEFI or Unified Extensible Firmware Interface no longer uses Option ROM which has to be upgraded anytime hardware is upgraded but uses drivers instead. BIOS was programmed using an assembler programming language and UEFI uses C. UEFI also boots faster than BIOS.https://phoenixts.com/blog/uefi-vs-legacy-bios/ UEFI no longer uses the POST and loads faster because of this. Unlike legacy BIOS, UEFI stores all initialization and startup in a .efi file. EFI File The EFI file holds boot loader programs for the operating system. UEFI Boot Process # The device is powered on # Firmware boot loaders initialize hardware # Firmware boot loaders boot the UEFI environment ## The Windows Boot Manager decides to ##* Boot to FFU flashing ##* Reset device ##* Update OS ##* Boot to OS # Bootloaders hand over control to UEFI applications written by #* SoC (Service Organzation Control) vendor #* Microsoft #* OEMs (Original Equipment Manufacturer)